System for stabilizing a visual display

ABSTRACT

A circuit for stabilizing the display on a cathode ray tube representing the position of transmitting beacons outlining the runway of an airport on which an aircraft is about to land. The beacons transmit pulses which are received by a receiver in the aircraft. Some of the transmitted pulses reflected from the ground are received simultaneously with the transmitted pulses and cause the display to bounce. The stabilizing circuit includes averaging circuits for averaging the transmitted and reflected pulses from each beacon to reduce the effect of the reflected pulses and stabilize the display. A read out control circuit periodically applies the averaged pulses to deflection means of a cathode ray tube. A synchronizing circuit controls the averaging circuits so that only the pulses from a single beacon are applied to the averaging circuits associated with the beacon.

Sttes atent Steinhauser [4 1 Mar. 28, 1972 SYSTEM FOR STABILIZING AVESUAL Primary Examiner-Richard A. Farley DISPLAY Assistan't Examiner-R.Kinberg Attorne -Plante, Hartz, Smith & Th so [72] Inventor: Hayes B.Steinhauser, Lincoln Park, N .J y omp n [73] Assignee: The BendixCorporation ABSTRACT [22] Filed: June 25,1969 A circuit for stabilizingthe display on a cathode ray tube I representing the position oftransmitting beacons outlining the [21] Appl 836352 runway of an airporton which an aircraft is about to land. The beacons transmit pulses whichare received by a receiver in 52 us. (:1 ..343/112, 325/42, 325/65, theaircraft some of the transmitted Pulses reflected from the 343/] 14.5ground are received simultaneously with the transmitted pul- [51] Int.Cl "G015 5/08 & and Cause the display to bounce. The stabilizing circuitin- [58] Field of Search ..343/l 14.5, 108 SM, 112; cludes averagingcircuits for averaging the transmitted and 325/65, 42 reflected pulsesfrom each beacon to reduce the effect of the reflected pulses andstabilize the display. [56] References Cited A read out control circuitperiodically applies the averaged UNITED STATES PATENTS pulses todeflection means of a cathode ray tube. A synchronizing circuit controlsthe averaging circuits so that 3237.195 2/1966 Schiffman ..343/1 12 onlythe pulses from a Single beacon are applied to the averag ing circuitsassociated with the beacon.

11 Claims, 4 Drawing Figures COUNTER one SHOT FLIP 3 CONTROL Q y PULSEE8 TRAIN E E M 3 332622 at???" E9 ll \mzewi'rs RECEIVER 4 EQA VERTICALPUliE TRAIN IZA E has READ OUT CONTROL CIRCUIT SMOOTHING |4 C IT CATHODERAY TU BE WFEmma I972 3,653 O48 SHEET 2 [1F 4 FIRST I BEACONS PULSESSECOND BEACON 'S PULSES THIRD BEACONS PULSES HORIZONTAL DEFLECTION PULSETN E3 TRAIN E4,

CONTROL PULSE START PULSE TRAIN EIOA SYNCH. I

INVENTOR. HAYES 6. STE/NHAUSER AI'I'ORNEV PAWNWMAM I972 3,653 O48 sum 30F 4 HEAD ou'r PULSE TRAIN E, V A A 7 V,

READ OUT PSLSE T MN EIZA V V READ OUT PULSE TRAlN E, v

AVERAGE HORIIZONTAL V V H F V n DEFLECTION v PULSES E AVERAGE SQQQWA lTL F1 F1 PULSES EBA AVERAGE I H H H n HORIZONTAL DEFLECTION PULSES EAVERAGE VERTICAL DEIFLECTION V PULSES EM AVERAGE VERTICAL H H H PULSESI4A AVERAGE VEWHCAL D FLECTION A V PULSES EMB BRIGHE'UP PULSE TRAIN E 2co M1? I N VENTOR.

HAYES 5. STE/NHAUSER ATIWRIVEY MIIEDIIIII 28 I972 3, 653 O48 SHEET I UF4 SYNCHRONIZING PULSE CIRCUIT I'll I I CONTROL PULSE ELECTRONIC ONE SHOTONE SHOT N L E TRAIN E6 SWITCH MULTIVIBRATOR MULTIVIBRATOR IEIO READ ourSMOOTHING CIRCUIT I8 PULSE I" I 37 45 I HCRIZONTAL v I ESIEEEE'ELECTRONIC ELECTRONIC EB I E I SWITCH SWITCH 3 I I 42 i l I I I L. j

E SYNCHRONIZING IO PULSE INVENTOR.

HAYES B. STE/NHAUSEP SYSTEM FOR STABILIZING A VISUAL DISPLAY BACKGROUNDOF THE INVENTION 1. Field of the Invention This invention pertains to amethod and apparatus for providing visual communication throughinclement weather particularly for an aircraft.

2. Description of the Prior Art Systems which aid in landing aircraft inall kinds of weather, such as disclosed in US. Pat. No. 3,237,195 issuedFeb. 22, 1966 to J. Schiffman and assigned to The Bendix Corporation,assignee of the present invention, uses microwave radio signals beamedto the aircraft by ground beacons located along each edge of a landingrunway. These signals are received on the aircraft and processed so asto form an edge light image of the runway on a special head-up cockpitdisplay which provides the pilot'with a picture of the runway similarto" i that formed by runway lights on a clear night.

The ground beacons operate independently of each other. Each beaconemits short microwave pulses at a repetition rate in the low audiorange, typically 120 c.p.s. These pulses are received on the aircraft bya special antenna system and microwave receiver which detects each pulseseparately and measures its angle of arrival both laterally andvertically, relative to aircraft boresight. These angles are translatedinto proportional horizontal and vertical deflection voltages whichposition a cathode ray tube beam to a corresponding angular position.The beam produces a bright spot on the cathode ray tube screen at aposition which, when viewed through the head-up viewer unit, will be atthe same angle as the angle of arrival of the pulse. The image on thecathode ray tube screen is projected optically onto a small viewingmirror in the pilots line of sight. Thus, the bright spot appears to theviewer to overlay the visual location of the beacon transmitting thatpulse, as seen through the cockpit window.

The spot representing a particular beacon is repeated on the CRT screeneach time a pulse is received from that beacon and, due to thepersistence of vision, appears without flicker. The presentation of thespots from all the ground beacons allows the pilot to see the pattern inwhich the ground beacons are arranged and results in a picture of therunaway as through outlined by lights at night. This display can be seenas well through fog and snow as in clear weather.

A radio frequency pulse from a ground beacon may reach the aircraftreceiver not only via the direct line of sight path, but also by variousreflection paths. At the low transmission angles encountered during alanding approach, the reflected path length will be very nearly the samelength as the direct line of sight path, particularly in the usual caseof reflection by the ground in front of the ground beacon. The time forthe pulse to travel from the beacon to the receiver depends on thelength of the transmission path. Thus, the reflected pulse will arriveat almost the same time as the direct pulse and may combine with thedirect pulse.

Since the angle of arrival of the reflected pulse is different than theangle of arrival of the direct pulse, the combination of the two willyield a different angle of arrival than the direct pulse alone.

The direct and reflected path lengths are continually changing during anapproach. The result is a bounce of the spot representing the beacon onthe cathode ray tube. The present invention provides a circuit and amethod for smoothing or averaging the spot position.

SUMMARY OF THE INVENTION In a system providing a display correspondingto a plurality of sources transmitting pulse trains of different phaseshaving a fixed repetition rate and in which the display bounces due toreflected pulses, means for stabilizing the display comprising means forreceiving the pulse trains. Means are connected to the receiving meansfor providing average pulses corresponding to pulses in each pulsetrain. Other means is connected to the receiving means and to theaverage pulse means for synchronizing each average pulse means with acorresponding pulse train. Means is connected to the average pulse meansfor providing the display in accordance with the average pulses.

One object of the present invention is to provide a system providing astabilized display.

Another object of the present invention is to provide a display systemusing average deflection pulses corresponding to transmitted pulses frombeacons to reduce the effect of reflected pulses on a display.

Another object of the present invention is to provide a dis play systemwhich distinguishes between different beacons transmitting in randomsequence but at a fixed repetition rate so that deflection pulsescorresponding to those beacons may be separated according to the beaconsand averaged.

Another object of the present invention is to provide a display systemwhich synchronizes itself with transmitted pulses from beacons. I V 7Another object of the present invention is to provide a display systemthat has an automatic self-starting synchronizing circuit whichperiodically restarts synchronization to achieve greater accuracy in thesynchronization.

Another object of the present invention is to provide a system fordisplaying dots corresponding to beacons transmitting pulses whicheliminates unwanted radar and other signals on the same frequency as thebeacons.

The foregoing and other objects and advantages of the invention willappear more fully hereinafter from a consideration of the detaileddescription which follows, taken together with the accompanying drawingswherein one embodiment of the invention is illustrated by way ofexample. It is to be expressly understood, however, that the drawingsare for illustration purposes only and are not to be construed asdefining the limits of the invention.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows a novel display systemconstructed in accordance with the present invention for displaying dotscorresponding to beacons outlining a runway of an airport. The number ofsynchronizing pulse circuits and smoothing circuits are reduced innumber so as not to confuse the drawing with undue multiplicity ofelements. The breaks, with respect to circuits having the suffix B," areintended to show that similar circuits in excess of the numberillustrated may be introduced within the broken portions by simpleextrapolation of the circuits illustrated.

FIG. 2 is a diagrammatic representation showing wave forms provided atvarious stages of operation of the display system shown in FIG. 1.

FIGS. 3 and 4 show a synchronizing pulse circuit and a smoothingcircuit, respectively, used in the display system of FIG. 1 to stabilizethe dot display.

DESCRIPTION OF THE INVENTION Referring to FIG. 1, there is shown a noveldisplay system with stabilization circuitry to eliminate the bounce in adot display of a landing runway at an airport, having antennae 3, 3A, 3Band 3C receiving transmitted pulses from three ground beacons, as shownin FIGS. 2A, 2B and 2C, and unwanted ground reflected pulses. Althoughsix beacons are used in most landing systems only three beacons areshown in the present application for the sake of simplicity. Antennae 3,3A, 3B and 3C are connected to a receiver 4 which provides a horizontaldeflection pulse train E;,, as shown in FIG. 2D, and a verticaldeflection pulse train E as shown in FIG. 2E, corresponding to thereceived pulses from the beacons as explained in the Schiffman patent.Receiver 4 also provides a control pulse train E as shown in FIG. 2F, inwhich the pulses coincide with each received pulse. In the Schiffmanpatent, the pulse train is used to brighten up the display, but in thepresent application is used for control purposes as hereinafterexplained.

The pulses in control pulse train E correspond to the beacons. With anall weather landing system using three beacons, the first three pulsescorrespond to the three beacons, as shown in FIGS. 2A, 2B, 2C and 2F.The pulses corresponding to a particular beacon always occur every thirdpulse after the initial pulse corresponding to that beacon, as shown inFIG. 2F.

Receiver 4 applies control pulse train E to a synchronizing networkwhich provides synchronizing pulse trains in response to control pulsetrain E for controlling pairs of smoothing circuits. Each pair ofsmoothing circuits provides average deflection pulses corresponding totransmitted pulses from a corresponding beacon as hereinafter explained.The synchronizing network includes an electronic switch 5, a counter 7,a one shot multivibrator l and a flip-flop 14 connected in series toreceiver 4 and a logic circuit 11 connecting identical synchronizingpulse Circuits 17, 17A and 178 to counter 7. Control pulse train E isapplied to switch 5 which controls the application of control pulsetrain E to counter 7. Initially switch 5 passes control pulse train ECounter 7 counts the pulses in the control pulse train E and provides aplurality of outputs to logic circuit 11 to start synchronizationprocess. Each output corresponds to a count in counter 7.

Logic circuit 11 applies start pulses E E and E as shown in FIGS. 2G, 2Hand 21, to synchronizing pulse circuits 17, 17A and 17B, respectively,in response to the outputs from counter 7. Each start pulse occurssimultaneously with a pulse in a corresponding pulse train from thebeacons as shown in FIGS. 2A, 2B, 2C, 20, 21-1 and 2I. Receiver 4 alsoapplies control pulse train E to pulse circuits 17, 17A and 17B. Pulsecircuits 17, 17A and 17B provide synchronizing pulse trains E E and E asshown in FIGS. 2], 2K and 2L, to control the smoothing circuits.

Referring to FIGS. 1 and 3, there is shown synchronizing pulse circuit17 including an electronic switch and one shot multivibrators 31 andconnected in series and an OR gate 33 connecting an output ofmultivibrator 35 to switch 30. Control pulse train E from receiver 4 isapplied to switch 30 and start pulse E from logic circuit 11 is appliedto OR gate 33. Switch 30 passes a pulse in control pulse train Ecorresponding to a pulse transmitted from the first beacon, in responseto start pulse E passed by OR gate 33. The passed pulse from switch 30triggers multivibrator 31. Start pulse E is terminated prior to anotherpulse in control pulse train E so that switch 30 is thereaftercontrolled by synchronizing pulse train E until the next start pulse EMultivibrator 31 provides a pulse having a pulse width corresponding tothe repetition rate of the transmitted pulses from the beacons forcontrolling the repetition rate of synchronizing pulse train E so thatpulse train E has the same repetition rate as the transmitted pulsesfrom the beacons. The termination of the pulse from multivibrator 31triggers multivibrator 35 causing multivibrator 35 to provide asynchronizing pulse E Synchronizing pulse E passes through OR gate 33and causes switch 30 to pass another pulse in control pulse train Ecorresponding to a pulse from the first beacon, to repeat the operationagain. Since multivibrator 31 was triggered by a pulse in control pulsetrain E corresponding to the first beacon, the time delay caused by thepulse from multivibrator 31 results in the pulses in synchronizing pulsetrain E occurring simultaneously with pulses corresponding to pulsesfrom the first beacon as shown in FIGS. 2A and 2,1.

Synchronizing pulse circuits 17A and 17B operate in a similar manner toprovide synchronizing pulse trains E and E respectively, that occursimultaneously with pulses transmitted by the other beacons as shown inFIGS. 2B, 2C, 2K and 2L.

Referring to FIG. 1, switch 5, counter 7, multivibrator 10 and flip-flop14 cooperate to automatically restart synchronization on a periodicbasis to assure a greater accuracy in the synchronization. Counter 7provides another output E to multivibrator 10 and to flip-flop 14corresponding to a predetermined count related to the number of beacons.

Flip-flop 14 applies a disable signal to switch 5 causing it to blockcontrol pulse train E in response to output E causing counter 7 to stopcounting. Multivibrator 10 applies a pulse to counter 7 and to'flip-flop14 whose width determines the time period for starting synchronizationagain. The termination of the pulse from multivibrator 10 resets counter7 and flip-flop l4. Flip-flop 14 then applies an enable signal to switch5 causing it to pass control pulse train E to counter 7 to start counter7 counting again which starts the synchronization as heretoforeexplained.

Synchronizing pulse circuit 17 applies synchronizing pulse train E toidentical smoothing circuits 18 and 19. Receiver 4 applies horizontaldeflection pulse train E and vertical deflection pulse train E tosmoothing circuits 18 and 19, respectively. Since pulses insynchronizing pulse train E occur simultaneously with the pulses fromthe first beacon, smoothing circuits 18 and 19 will provide deflectionpulsesE and E respectively, as shown in FIGS. 20 and 2U, correspondingto the average of the horizontal deflection pulses and the average ofthe vertical deflection pulse, respectively, related to the transmittedpulses from the first beacon. The effect of the reflected pulses on thedeflection pulses corresponding to the first beacon is reduced bysmoothing circuits 18 and 19. A read out control circuit continuouslyprovides read out pulse train E,,, as shown in FIG. 2M, during operationof the display system to smoothing circuits 18 and 19.

Referring to FIGS. 1 and 4, smoothing circuit 18 includes seriallyconnected electronic switches 37 and 45 and a variable resistor 40connected to receiver 4. Smoothing circuit 18 also includes a capacitor41 and a variable resistor 42 connected to an input to switch 45 and toground. Switch 37 receives horizontal deflection pulse train E, fromreceiver 4 and synchronizing pulse train E from pulse circuit 17 andpasses only those pulses of deflection pulse train E corresponding tothe transmitted pulses from the first beacon in response tosynchronizing pulse train E The passed pulses charge up capacitor 41which partially discharge through resistor 42 between passed pulses toprovide a voltage level which is proportional to the average level ofthe passed pulses. This level will vary at a much slower rate than thevariations in level of the incoming pulses, thus providing a smoothingeffeet. The number of pulses that are averaged is controlled by theresistance value of resistors 40 and 42. Switch 45 is controlled byreadout pulse train E from read out control circuit 20 to pass thevoltage across capacitor 41 as average horizontal deflection pulses ESmoothing circuit 19 operates in a similar manner to provide averagevertical deflection pulses E which occur simultaneously with averagehorizontal deflection pulses E as shown in FIGS. 20 and 2T.

Referring to FIG. 1, receiver 4 applies horizontal deflection pulsetrain E to smoothing circuits 18A'and 18B and vertical deflection pulsetrain E to-srnoothing circuits 19A and 19B. Synchronizing pulse circuits17A and 17 B apply synchronizing pulse trains E and E to smoothingcircuits 18A and 19A and 18B and 198, respectively. Read out controlcircuit 20 applies read out pulse trains E and E as shown in FIGS. 2Nand 21, to smoothing circuits 18A and 19A, and 18B and 198,respectively. Smoothing circuits 18A, 18B, 19A and 19B are identical tosmoothing circuit 18 and operate in a similar manner. Smoothing circuits18A and 19A provide simultaneous average deflection pulses E and Erespectively, as shown in FIGS. 2R and 2U. Smoothing circuits 18B and1913 provide simultaneous average deflection pulses E and Erespectively, as shown in FIGS. 28 and 2V.

The average horizontal and vertical deflection pulses, from thesmoothing circuits cause a cathode ray tube 24, having a face 27, toprovide a stabilized clot display on the face 27 giving a visualimpression of the runway. Cathode ray tube 24 has a horizontaldeflection plate 25 connected to smoothing circuit 18, 18A and 18B and avertical deflection plate 26 connected to smoothing circuit 19, 19A and19B. Tube 25 also has a horizontal deflection plate 28 and a verticaldeflection plate 29 connected to ground. Read out control circuit 20also provides a bright up pulse train E to a grid 29 of tube 24 forbrightening up the display.

The present invention, as heretofore described, provides a stabilizeddisplay of dots corresponding to beacons outlining a runway of anairport. The present invention synchronizes itself with the transmissionof pulses from the beacons so that deflection pulses corresponding tothe beacons can be averaged to provide the stabilized dot display byreducing the effect of reflected pulses. The synchronization of thepresent invention with the transmitted pulses from the beacons isautomatically self-started on a periodic basis to increase the accuracyof the synchronization. The present invention also eliminates the effectof radar and other unwanted signals on the same frequency as thebeacons.

Although but a single embodiment of the invention has been illustratedand described in detail, it is to be expressly understood that theinvention is not limited thereto. Various changes may also be made inthe design and arrangement of the parts without departing from thespririt and scope of the invention as the same will now be understood bythose skilled in the art.

What is claimed is:

l. In a system providing a display corresponding to the position of aplurality of sources transmitting pulse trains of different phases andin which the display bounces due to reflected pulses, means forstabilizing the display comprising means for receiving the pulse trains,means connected to the receiving means for providing average pulsescorresponding to pulses in each pulse train, means connected to thereceiving means and to the average pulse means for synchronizing eachaverage pulse means with a corresponding pulse train, and meansconnected to the average pulse means for providing the display inaccordance with the average pulses.

2. Stabilizing means of the kind described in claim 1 in which thereceiving means provides deflection pulses corresponding to the pulsesin each pulse train, and a control pulse train for each pulse in thepulse trains.

3. A display system of the kind described in claim 2 in which thesynchronizing means includes means for automatically startingsynchronization in response to the control pulses from the receivingmeans.

4. A display system of the kind described in claim 3 in which theautomatic starting means includes means for counting the control pulsesfrom the receiving means and providing an output corresponding to acount in the counting means, means connecting the receiving means to thecounting means for controlling the starting and stopping of the countingmeans, a logic circuit connected to the counting means and responsive tothe output from the counting means to provide a plurality of startpulses, each start pulse corresponding to a different received pulsetrain, and means connected to the receiving means, to the logic circuitand to the averaging means, for providing synchronizing pulse trains,each synchronizing pulse train means provides a synchronizing pulsetrain in phase with a corresponding received pulse train in accordancewith a start pulse from the logic circuit and the control pulses fromthe receiving means related to the corresponding pulse train.

5. A system of the kind described in claim 4 in which each synchronizingpulse train means includes a switching means connected to the receivingmeans and to the logic circuit for passing the control pulses from thereceiving means in response to a start pulse from the logic circuit orblocking the control pulses during the absence of a start pulse, a oneshot multivibrator connected to the said switching means and responsiveto a passed control pulse from the said switching means to provide adelay pulse having a pulse width cor responding to the repetition rateof the received pulse trains, and another one shot multivibratorconnected to the average pulse means, to the said switching means and tothe other multivibrator and responsive to the termination of the pulsefrom the other multivibrator to provide a pulse to the said switchingmeans and to the average pulse means to cause the said switching meansto pass another pulse from the receiving means to the othermultivibrator so as to continuously recycle the operation of thesynchronizing pulse train means to provide a synchronizin pulse train tothe average pulse means 6. A system oft e kind described in claim 4 inwhich the deflection pulses from the receiving means include horizontaland vertical deflection pulses and the average pulse means includes aplurality of circuits, each circuit including a pair of networksconnected to the receiving means and to a corresponding synchronizingpulse train means, one network receiving horizontal deflection pulsesfrom the receiving means and the other network receiving verticaldeflection pulses from the receiving means, each network including yetanother switching means connected to the receiving means for passing thedeflection pulses from the receiving means in response to pulses in asynchronizing pulse train from the corresponding synchronizing pulsetrain means and blocking the deflection pulses between pulses in thesynchronizing pulse train, and an averaging circuit connected to thelast mentioned switching means for averaging the passed deflectionpulses from the last mentioned switching means and providing an outputcorresponding to the average of the deflection pulses corresponding to areceived pulse train; and means connected to the averaging circuit ineach network for providing the average deflection pulses in accordancewith the outputs from the averaging circuits in the networks.

7. A system of the kind described in claim 6 in which each averagingcircuit includes a capacitor, a resistor connecting the last mentionedswitching means to the capacitor and controlling the charging of thecapacitor by the passed deflection pulses, and another resistorconnected so as to shunt the capacitor and controlling the dischargerate of the capacitor so that the capacitor provides the outputcorresponding to the average of the passed deflection pulses.

8. A system of the kind described in claim 6 in which the average pulsemeans includes a plurality of switches. each switch connected to theaveraging circuit in a different network, and means connected to theswitches for periodically applying read out pulses to positively controlthe switches to pass the outputs from the averaging circuits as pulsesto provide the average deflection pulses.

9. A display system of the kind described in claim 4, in which thecontrol means includes switching means connecting the receiving means tothe counting means for passing the control pulses to the counting meansfrom the receiving means until a command signal is applied to theswitching means and blocking the control pulses from the receiving meansin response to the c command signal, and a flip-flop connected to thecounting means and to the switching means for providing the commandsignal in response to an output from the counting means corresponding toa count equal to the number of pulse train sources.

10. A display system of the kind described in claim 9 in which thesynchronizing means also includes means for restarting synchronizationon a periodic basis.

11. A display system of the kind described in claim 10 in which therestarting means includes a monostable multivibrator connected to thecounting means and to the flip-flop and providing a delay pulse inresponse to the output from the counting means corresponding to thenumber of pulse train sources to reset the counting means and theflip-flop to restart the counting of the counting pulses from thereceiving means by the control means after a predetermined time periodhas elapsed.

1. In a system providing a display corresponding to the position of aplurality of sources transmitting pulse trains of different phases andin which the display bounces due to reflected pulses, means forstabilizing the display comprisiNg means for receiving the pulse trains,means connected to the receiving means for providing average pulsescorresponding to pulses in each pulse train, means connected to thereceiving means and to the average pulse means for synchronizing eachaverage pulse means with a corresponding pulse train, and meansconnected to the average pulse means for providing the display inaccordance with the average pulses.
 2. Stabilizing means of the kinddescribed in claim 1 in which the receiving means provides deflectionpulses corresponding to the pulses in each pulse train, and a controlpulse train for each pulse in the pulse trains.
 3. A display system ofthe kind described in claim 2 in which the synchronizing means includesmeans for automatically starting synchronization in response to thecontrol pulses from the receiving means.
 4. A display system of the kinddescribed in claim 3 in which the automatic starting means includesmeans for counting the control pulses from the receiving means andproviding an output corresponding to a count in the counting means,means connecting the receiving means to the counting means forcontrolling the starting and stopping of the counting means, a logiccircuit connected to the counting means and responsive to the outputfrom the counting means to provide a plurality of start pulses, eachstart pulse corresponding to a different received pulse train, and meansconnected to the receiving means, to the logic circuit and to theaveraging means, for providing synchronizing pulse trains, eachsynchronizing pulse train means provides a synchronizing pulse train inphase with a corresponding received pulse train in accordance with astart pulse from the logic circuit and the control pulses from thereceiving means related to the corresponding pulse train.
 5. A system ofthe kind described in claim 4 in which each synchronizing pulse trainmeans includes a switching means connected to the receiving means and tothe logic circuit for passing the control pulses from the receivingmeans in response to a start pulse from the logic circuit or blockingthe control pulses during the absence of a start pulse, a one shotmultivibrator connected to the said switching means and responsive to apassed control pulse from the said switching means to provide a delaypulse having a pulse width corresponding to the repetition rate of thereceived pulse trains, and another one shot multivibrator connected tothe average pulse means, to the said switching means and to the othermultivibrator and responsive to the termination of the pulse from theother multivibrator to provide a pulse to the said switching means andto the average pulse means to cause the said switching means to passanother pulse from the receiving means to the other multivibrator so asto continuously recycle the operation of the synchronizing pulse trainmeans to provide a synchronizing pulse train to the average pulse means.6. A system of the kind described in claim 4 in which the deflectionpulses from the receiving means include horizontal and verticaldeflection pulses and the average pulse means includes a plurality ofcircuits, each circuit including a pair of networks connected to thereceiving means and to a corresponding synchronizing pulse train means,one network receiving horizontal deflection pulses from the receivingmeans and the other network receiving vertical deflection pulses fromthe receiving means, each network including yet another switching meansconnected to the receiving means for passing the deflection pulses fromthe receiving means in response to pulses in a synchronizing pulse trainfrom the corresponding synchronizing pulse train means and blocking thedeflection pulses between pulses in the synchronizing pulse train, andan averaging circuit connected to the last mentioned switching means foraveraging the passed deflection pulses from the last mentioned switchingmeans and providing an output corresponding to the average of thedeflection pulses correSponding to a received pulse train; and meansconnected to the averaging circuit in each network for providing theaverage deflection pulses in accordance with the outputs from theaveraging circuits in the networks.
 7. A system of the kind described inclaim 6 in which each averaging circuit includes a capacitor, a resistorconnecting the last mentioned switching means to the capacitor andcontrolling the charging of the capacitor by the passed deflectionpulses, and another resistor connected so as to shunt the capacitor andcontrolling the discharge rate of the capacitor so that the capacitorprovides the output corresponding to the average of the passeddeflection pulses.
 8. A system of the kind described in claim 6 in whichthe average pulse means includes a plurality of switches, each switchconnected to the averaging circuit in a different network, and meansconnected to the switches for periodically applying read out pulses topositively control the switches to pass the outputs from the averagingcircuits as pulses to provide the average deflection pulses.
 9. Adisplay system of the kind described in claim 4, in which the controlmeans includes switching means connecting the receiving means to thecounting means for passing the control pulses to the counting means fromthe receiving means until a command signal is applied to the switchingmeans and blocking the control pulses from the receiving means inresponse to the command signal, and a flip-flop connected to thecounting means and to the switching means for providing the commandsignal in response to an output from the counting means corresponding toa count equal to the number of pulse train sources.
 10. A display systemof the kind described in claim 9 in which the synchronizing means alsoincludes means for restarting synchronization on a periodic basis.
 11. Adisplay system of the kind described in claim 10 in which the restartingmeans includes a monostable multivibrator connected to the countingmeans and to the flip-flop and providing a delay pulse in response tothe output from the counting means corresponding to the number of pulsetrain sources to reset the counting means and the flip-flop to restartthe counting of the counting pulses from the receiving means by thecontrol means after a predetermined time period has elapsed.